1. Field of the Invention
The present invention relates to a semiconductor laser unit used in an optical head device or the like and to a method for manufacturing an optical reflection film.
2. Description of the Related Art
For example, an optical head device is constituted with a semiconductor laser unit for emitting laser beams to a target optical disk, a light-receiving element for receiving the laser beams returned by being reflected at the optical disk, a signal processing circuit and the like for processing electric signals that are generated at the light-receiving element according to the received laser beams. The semiconductor laser unit outputs the laser beams to the outside of the device by reflecting it with a mirror part.
Recently, in order to reduce the size of the device and to simplify alignment control of each optical element, a type in which the semiconductor laser unit, the light-receiving element, and the signal processing circuit are loaded on a single semiconductor substrate has been developed, as disclosed in Japanese Published Patent Literature 1 (Japanese Unexamined Patent Publication 64-27288: pp. 2-3, FIG. 1), for example.
On the occasion of forming the semiconductor laser unit and the light-receiving element on the same substrate as mentioned above, highly positioning accuracy is required at the time of forming the semiconductor laser unit. That is, unless the relative positions of the semiconductor laser unit and the optical disk as a target of irradiating the laser beams are aligned with high precision, there causes a problem in functions of the device.
In order to secure the mounting accuracy of the semiconductor laser unit, as disclosed in Japanese Published Patent Literature 2 (Japanese Unexamined Patent Publication 9-326535: p. 6, FIG. 1), a technique in which grooves are formed on the substrate in advance has been developed so that the bump electrodes of the semiconductor laser element as the emission source of the laser beams can be fitted into the grooves.
In the techniques disclosed in Japanese Published Patent Literatures 1 and 2, the semiconductor laser beams are assumed to be red-infrared rays with the wavelengths of 600 nm-1200 nm, and an Au film is used therein as the optical reflection film. Thus, the reflectivity of the blue rays becomes low in the optical reflection film formed in this manner, and thereby the use efficiency of the light is decreased. Further, when a semiconductor laser emitting blue rays is used, the reflectivity at the Au film becomes deteriorated compared to the case of the red-infrared rays due to the material property. Thus, the intensity of the emitted laser beams becomes attenuated. As a measure for securing the sufficient property for the blue rays, the optical reflection film may be formed as a multilayer film of an Al layer and a dielectric layer. However, in that case, the reflectance of the red-infrared rays becomes lower compared to the one of the Au film, thereby deteriorating the use efficiency of the light. Like this, when the laser beams of blue-infrared rays are emitted simultaneously, the reflectance of either light becomes deteriorated. Structure of the reflection film that corresponds to the wavelength range of the blue-infrared rays and process for achieving it have not yet been proposed so far.
The present invention has been invented to solve such problems, and the object of the present invention therefore is to provide a semiconductor laser unit whose reflectance is excellent for the laser emission light over a wide wavelength area of the blue-infrared rays.